Are the PDF's made directly from the electronic page layouts (pre-press) or are they merely scans of the printed pages saved as PDF? I have scans of the article I need but would prefer to pay for 'source' PDF version.

The PDFs are the actual files that go to print, though reduced from 300dpi to 75 dpi for download size and web view. In other words, you can clearly read, print and bind them, but you wouldn't be able to get press quality print from them.